Lighting system with thermal management system

ABSTRACT

Lighting systems having unique configurations are provided. For instance, the lighting system may include a light source, a thermal management system and driver electronics, each contained within a housing structure. The light source is configured to provide illumination visible through an opening in the housing structure. The thermal management system is configured to provide an air flow, such as a unidirectional air flow, through the housing structure in order to cool the light source. The driver electronics are configured to provide power to each of the light source and the thermal management system.

CROSS REFERENCE TO RELATED APPLICATION

The present invention is a continuation of, and claims priority to, U.S.patent application Ser. No. 13/887,793, filed May 6, 2013, which is acontinuation of, and claims priority to, U.S. patent application Ser.No. 12/711,000, filed Feb. 23, 2010, now U.S. Pat. No. 8,434,906, thedisclosures of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

This invention was made with Government support under contract numberDE-FC26-08NT01579 awarded by The United States Department of Energy. TheGovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

The invention relates generally to lighting systems, and moreparticularly to lighting systems having thermal systems.

High efficiency lighting systems are continually being developed tocompete with traditional area lighting sources, such as incandescent orflorescent lighting. While light emitting diodes (LEDs) havetraditionally been implemented in signage applications, advances in LEDtechnology have fueled interest in using such technology in general arealighting applications. LEDs and organic LEDs are solid-statesemiconductor devices that convert electrical energy into light. WhileLEDs implement inorganic semiconductor layers to convert electricalenergy into light, organic LEDs (OLEDs) implement organic semiconductorlayers to convert electrical energy into light. Significant developmentshave been made in providing general area lighting implementing LEDs andOLEDs.

One potential drawback in LED applications is that during usage, asignificant portion of the electricity in the LEDs is converted intoheat, rather than light. If the heat is not effectively removed from anLED lighting system, the LEDs will run at high temperatures, therebylowering the efficiency and reducing the reliability of the LED lightingsystem. In order to utilize LEDs in general area lighting applicationswhere a desired brightness is required, thermal management systems toactively cool the LEDs may be considered. Providing an LED-based generalarea lighting system that is compact, lightweight, efficient, and brightenough for general area lighting applications is challenging. Whileintroducing a thermal management system to control the heat generated bythe LEDs may be beneficial, the thermal management system itself alsointroduces a number of additional design challenges.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a lighting system is provided. The lighting systemincludes a housing structure. The lighting system further includes alight source configured to provide illumination visible through anopening in the housing structure. Still further, the lighting systemincludes a thermal management system configured to provide aunidirectional air flow through the housing structure. Additionally, thelighting system includes driver electronics configured to provide powerto each of the light source and the thermal management system.

In another embodiment, a lighting system is provided that includes anarray of light emitting diodes (LEDs) arranged on a surface of alighting plate. The lighting system further includes a thermalmanagement system arranged above the array of LEDs, wherein the thermalmanagement system comprises a plurality of synthetic jet devices,wherein each of the plurality of synthetic jet devices is configured toproduce a jet stream in a direction parallel to the surface of thelighting plate.

In another embodiment, a method of cooling a lighting system isprovided. The method includes illuminating a plurality of lightingelements arranged on a planar surface of the lighting system,transferring heat from the plurality of lighting elements to a heatsink, and driving air from an area outside of the lighting systemthrough the lighting system and back out to the area outside of thelighting system.

In another embodiment, a lighting system is provided, wherein thelighting system includes an Edison base configured to couple toelectrically couple to a standard light socket, a light source and athermal management system. The thermal management system includespassive cooling components and active cooling components.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is block diagram of a lighting system in accordance with anembodiment of the invention;

FIG. 2 illustrates a perspective view of a lighting system, inaccordance with an embodiment of the invention;

FIG. 3 illustrates an exploded view of the lighting system of FIG. 2, inaccordance with an embodiment of the invention;

FIG. 4 illustrates the airflow of a thermal management system of thelighting system of the FIGS. 2 and 3, in accordance with an embodimentof the invention;

FIG. 5 illustrates a perspective view of the light source of thelighting system of FIGS. 2 and 3, in accordance with an embodiment ofthe invention;

FIG. 6 illustrates a layout design of the light source of FIG. 5, inaccordance with an embodiment of the invention;

FIG. 7 illustrates a schematic diagram of a circuit configured toprovide power to the lighting source of FIG. 5, in accordance with anembodiment of the invention; and

FIG. 8 illustrates a schematic diagram of a circuit configured toprovide power to the thermal management system, in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention generally relate to LED-based area lightingsystems. A novel luminaire is provided with driver electronics, LEDlight source and an active cooling system, which includes syntheticjets. In one embodiment, the lighting system fits into a standard 6″(15.2 cm) halo and leaves approximately 0.5″ (1.3 cm) between the lampand halo. Alternatively, the lighting system may be scaled differently,depending on the application. The presently described embodimentsprovide a lighting source, which produces approximately 1500 lumens (lm)with a driver electronics efficiency of 90%, and may be useful in arealighting applications. The thermal management system includes syntheticjet cooling which provides an air flow in and out of the lightingsystem, allowing LED junction temperatures to remain less than 100° C.for the disclosed embodiments. To reach 1500 lm, the disclosed lightsource utilizes blue LEDs and a phosphor mixture that results in acorrelated color temperature (CCT) of approximately 3000° Kelvin and acolor rendering index (CRI) of over 82. For example, in one embodiment,the light source may utilize 19 LEDs.

Advantageously, in one embodiment, the lighting system uses aconventional screw-in base (i.e., Edison base) that is connected to theelectrical grid. The electrical power is appropriately supplied to thethermal management system and to the light source by the same driverelectronics unit. In one embodiment, the LEDs of the light source aredriven at 500 mA and 59.5 V while the synthetic jets of the thermalmanagement system are driven with less than 200 Hz and 64 V(peak-to-peak). The LEDs provide a total of over 1500 steady state facelumens, which is sufficient for general area lighting applications. Inthe illustrated embodiments described below, five synthetic jet devicesare provided to work in conjunction with a heat sink having a pluralityof fins, and air ports, to both actively and passively cool the LEDs. Aswill be described, the synthetic jet devices are excited with a desiredpower level to provide adequate cooling during illumination of the LEDs.

Accordingly, embodiments of the invention provide a unique compactlighting system capable of efficiently providing a desired level oflight for area lighting applications, utilizing a reduced number ofLEDs, compared to conventional systems. The disclosed thermal managementsystem provides air flow from outside of the housing structure, throughthe lighting system, and back into the ambient air. In one embodiment,the air flow is unidirectional, as will be described further below. Byusing the active cooling technology of synthetic jets, in combinationwith the passive heat sink and air ports described below, embodiments ofthe invention provide an inexpensive lighting system capable ofproducing 1500 lumens, with a reduced number of LEDs.

Referring now to FIG. 1, a block diagram illustrating a lighting system10 in accordance with embodiments of the present invention isillustrated. In one embodiment, the lighting system 10 may be ahigh-efficiency solid-state down-light luminaire. In general, thelighting system 10 includes a light source 12, a thermal managementsystem 14, and driver electronics 16 configured to drive each of thelight source 12 and the thermal management system 14. As discussedfurther below, the light source 12 includes a number of LEDs arranged toprovide down-light illumination suitable for general area lighting. Inone embodiment, the light source 12 may be capable of producing at leastapproximately 1500 face lumens at 75 lm/W, CRI>80, CCT=2700 k-3200 k,50,000 hour lifetime at a 100° C. LED junction temperature. Further, thelight source 12 may include color sensing and feedback, as well as beingangle control.

As will also be described further below, the thermal management system14 is configured to cool the LEDs such that the LED junctiontemperatures remain at less than 100° C. under normal operatingconditions. In one embodiment, the thermal management system 14 includessynthetic jet devices 18, heat sinks 20 and air ports 22 which areconfigured to work in conjunction to provide the desired cooling and airexchange for the lighting system 10.

The driver electronics 16 includes an LED power supply 24 and asynthetic jet power supply 26. As will be described further below, inaccordance with one embodiment, the LED power supply 24 and thesynthetic jet power supply 26 each comprise a number of chips andintegrated circuits residing on the same system board, such as a printedcircuit board (PCB), wherein the system board for the driver electronics16 is configured to drive the light source 12, as well as the thermalmanagement system 14.

Referring now to FIG. 2, a perspective view of one embodiment of thelighting system 10 is illustrated. In one embodiment, the lightingsystem 10 includes a conventional screw-in base (Edison base) 30 thatmay be connected to a conventional socket that is coupled to theelectrical power grid. The system components are contained within ahousing structure generally referred to as a housing structure 32. Aswill be described and illustrated further with regard to FIG. 3, thehousing structure 32 is configured to support and protect the internalportion of the light source 12, the thermal management system 14, andthe driver electronics 16.

In one embodiment, the housing structure 32 includes a cage 34, havingair slots 36 there through. The cage 34 is configured to protect theelectronics board having the driver electronics 16 disposed thereon. Thehousing structure 32 further includes a thermal management systemhousing 38 to protect the components of the thermal management system14. In accordance with one embodiment, the thermal management systemhousing 38 is shaped such that air ports 22 allow ambient air to flow inand out of the lighting system 10 by virtue of synthetic jets in thethermal management system 14, as described further below. Further, thehousing structure 32 includes a faceplate 40 configured to support andprotect the light source 12. As will be described and illustrated inFIG. 3, the faceplate 40 includes an opening which is sized and shapedto allow the faces of the LEDs 42 and/or optics, of the light source 12,to be exposed at the underside of the lighting system 10 such that whenilluminated, the LEDs 42 provide general area down-lighting.

Turning now to FIG. 3, an exploded view of the lighting system 10 isillustrated. As previously described and illustrated, the lightingsystem 10 includes a housing structure 32 which includes the cage 34,the thermal management system housing 38, and the faceplate 40. Whenassembled, the housing structure 32 is secured by screws 44 configuredto engage the cage 34, the thermal management system housing 38, and aholding mechanism such as a plurality of nuts 46. In one embodiment, thefaceplate 40 is sized and shaped to frictionally engage a base of thelighting system 10, and/or secured by another fastening mechanism suchas additional screws (not shown). An opening 48 in the faceplate 40 issized and shaped such that the LEDs 42 positioned on the underside ofthe light source 12 may be visible to the opening 48. The light source12 may also include fastening components, such as pins 50 configuredengage an underside of the thermal management system 14. As will beappreciated, any variety of fastening mechanisms may be included tosecure the components of the lighting system 10, within the housingstructure 32, such that the lighting system 10 is a single unit, onceassembled for use.

As previously described, the driver electronics 16 which are housedwithin the cage 34 include a number of integrated circuit components 52mounted on a single board, such as a printed circuit board (PCB) 54. Aswill be appreciated, the PCB 54 having components mounted thereto, suchas the integrated circuit components 52, forms a printed circuitassembly (PCA). Conveniently, the PCB 54 is sized and shaped to fitwithin the protective cage 34. Further, the PCB 54 includesthrough-holes 56 configured to receive the screws 44 such that thedriver electronics 16, the thermal management system housing 38, and thecage 34 are mechanically coupled together. In accordance with thepresently described embodiment, all of the electronics configured toprovide power for the light source 12, as well as the thermal managementsystem 14 are contained on a single PCB 54, which is positioned abovethe thermal management system 14 and light source 12. Thus, inaccordance with the present design, the light source 12 and the thermalmanagement system 14 share the same input power.

In the illustrated embodiment, the thermal management system 14 includesa heat sink 20 having a number of fins 58 coupled to a base 60 viascrews 62. As will be appreciated, the heat sink 20 provides aheat-conducting path for the heat produced by the LEDs 42 to bedissipated. The base 60 of the heat sink 20 is arranged to rest againstthe backside of the light source 12, such that heat from the LEDs 42 maybe transferred to the base 60 of the heat sink 20. The fins 58 extendperpendicularly from the base 60, and are arranged to run parallel toone another.

The thermal management system 14 further includes a number of syntheticjet devices 18 which may be mounted on the fins 58 of the heat sink 20.As will be appreciated, each synthetic jet device 18 is configured toprovide a synthetic jet flow to provide further cooling of the LEDs 48.Each synthetic jet device 18 includes a diaphragm 64 which is configuredto be driven by the synthetic jet power supply 26 such that thediaphragm 64 moves rapidly back and forth within a hollow frame 66 tocreate an air jet through an opening in the frame 66 which will bedirected through the gaps between the fins 58 of the heat sink 20. Thesynthetic jet devices 18 may include tabs 68, having holes therethrough,such that pins 69 may be used to secure each synthetic jet device 18 toa respective fin 58. The thermal management system 14 and theunidirectional airflow created by these synthetic jet devices 18 will bedescribed further below with respect to FIG. 4.

Referring now to FIG. 4, a partial cross-sectional view of the lightingsystem 10 is provided to illustrate certain details of the thermalmanagement system 14. As previously discussed, the thermal managementsystem 14 includes synthetic jet devices 18, heat sink 20, and air ports22. The base 60 of the heat sink 20 is arranged in contact with theunderlying light source 12, such that heat can be passively transferredfrom the LEDs 42 to the heat sink 20. The array of synthetic jet devices18 is arranged to actively assist in the linear transfer of heattransfer, along the fins 58 of the heat sink 20. In the illustratedembodiment, one synthetic jet device 18 is positioned within therecesses provided by the gaps between the parallel fins 58. Thesynthetic jet devices 18 can be powered to create a unidirectional flowof air inside the heat sink 20, between the fins 58, such that air fromthe surrounding area is entrained into the duct through one of the ports22A and warm air from the heat sink 20 is ejected into the ambient airthrough the other port 22B. The unidirectional airflow into the port 22Athrough the fin gaps and out the port 22B is generally indicated byairflow arrows 70. Advantageously, the unidirectional air flow 70prevents heat buildup within the lighting system 10, which is a leadingcause for concern in the design of thermal management of down-lightsystems. In alternative embodiments, the air flow created by thesynthetic jet devices 18 may be radial or impinging, for instance. Thepresently described thermal management system 14 is capable of providingan LED junction temperature of less than 100° C. at approximately 30 Wof heat generation.

As will be appreciated, synthetic jets, such as the synthetic jetdevices 18, are zero-net-massflow devices that include a cavity orvolume of air enclosed by a flexible structure and a small orificethrough which air can pass. The structure is induced to deform in aperiodic manner causing a corresponding suction and expulsion of the airthrough the orifice. The synthetic jet 18 imparts a net positivemomentum to its external fluid, here ambient air. During each cycle,this momentum is manifested as a self-convecting vortex dipole thatemanates away from the jet orifice. The vortex dipole then impinges onthe surface to be cooled, here the underlying light source 12,disturbing the boundary layer and convecting the heat away from itssource. Over steady state conditions, this impingement mechanismdevelops circulation patterns near the heated component and facilitatesmixing between the hot air and ambient fluid.

In accordance with one embodiment, each synthetic jet devices 18 has twopiezoelectric disks, excited out of phase and separated by a thincompliant wall with an orifice. This particular design has demonstratedsubstantial cooling enhancement, during testing of the disclosed design.It is important to note that the synthetic jet operating conditionsshould be chosen to be practical within lighting applications. Thepiezoelectric components are similar to piezoelectric buzzer elements.The package that holds the synthetic jet 18 in the luminaire shouldorient it for maximum cooling effectiveness without mechanicallyconstraining the motion of the synthetic jet. The cooling performanceand operating characteristics of the synthetic jet device 18 are due tothe interaction between several physical domains includingelectromechanical coupling in the piezoelectric material used foractuation, structural dynamics for the mechanical response of theflexible disks to the piezoelectric actuation, and fluid dynamics andheat transfer for the jet of air flow 70. Sophisticated finite element(FE) and computational fluid dynamics (CFD) software programs are oftenused to simulate the coupled physics for synthetic jet design andoptimization.

Referring now to FIG. 5, a light source 12 in accordance with oneembodiment of the invention is illustrated. As illustrated, the lightsource 12 includes a number of LEDs 42 arranged on a plate 72. Inaccordance with one embodiment, the light source 12 may include nineteen(19) blue LEDs 42. For example, each blue LED may be a CREE EZ 1000, 470nm chip. Each LED 42 utilizes YAG phosphor for warm light conversion.Each LED 42 may also include an intermediate silicone molded lambertainlens. The presently described layout was tested and resulted in 1500 lmwith a 25° full width half max optics being possible at 55 LPW, 3000 Kand CRI of 82 with the nineteen blue LEDs 42. As will be appreciated,the light source 12 is in thermal communication with the heat sink 20 bya highly thermally-conductive interface.

As will be appreciated, various types of LEDs 42 may be employed.Further, with increased drive capabilities, the number of LEDs 42 in thelight source 12 may be reduced. In general, utilizing LEDs 42 that areprovided as bare die provides a small light source 12, reduced opticalsize, and easy interchangeability of the individual LEDs 42. FIG. 6illustrates one design layout of the light source 12, as utilized in theembodiment of FIG. 5. As illustrated, each individual LED 42 may bepositioned onto a hexagonal footprint 74 and arranged in a honeycombpattern to minimize the overall footprint of the LED array. Inaccordance with one embodiment, the circumference of the array (C_(A))is approximately equal to 75 mm. The circumference of the plate 72(C_(P)) may be approximately 130 mm. Further, the long width (W_(L)) andthe short width (W_(S)) may be equal to approximately 57 mm and 49.5 mm,respectively. As will be appreciated, various sizes and dimensions ofthe LEDs 42 and overall light source 12 may be employed.

As previously described, the driver electronics 16 include an LED powersupply 24 and a synthetic jet power supply 26. In one embodiment, theelectronics for each component of the driver electronics 16 are providedon a single printed circuit board 54 (FIG. 3). Any number of designs forthe driver electronics 16 may be employed to achieve a desired result ofa high efficiency lighting system 10 capable of providing at leastapproximately 1500 lm using the LEDs 42. As described further below,FIG. 7 illustrates one embodiment of the LED power supply 24 and FIG. 8illustrates one embodiment of the synthetic jet power supply 26, whichhave been tested for use in the embodiments of the invention, and whichhave proven acceptable for driving the light source 12 and thermalmanagement system 14.

Specifically, the illustrated schematic diagram of FIG. 7 is capable ofdriving the light source 12 such that the lighting system 10 has anefficiency of greater than 90%, a power factor greater than or equal to0.9, galvanic isolation between input AC voltage and output voltage, andan input voltage of 120 V RMS at 60 Hz. As is well known, theillustrated LED power supply 24 includes a fly back converter topology.The fly back topology provides isolation and also adjustment of voltageconversion ratios through the turns ratios of the constituenttransformer. The switching frequency of the LED power supply circuit 24can be chosen in the low 100 kHz in order to affect reduction in size ofthe passive components. The circuit of FIG. 8 proved acceptable inproviding sufficient drive conditions for the synthetic jets 18 of thethermal management system 14 described above. Those skilled in the artwill appreciate that any number of circuits may be employed in thelighting system 10, in order to meet the preferred system requirementsfor driving each of the light source 12 and thermal management system14.

Test Data and Example Circuit Designs

In choosing an acceptable circuit design for the LED power supply 24,designs meeting the following parameters were considered.

-   -   Efficiency of ≧90%.    -   Power Factor ≧0.9 for commercial applications, ≧0.7 for        Residential applications.    -   Input voltage of 120 V RMS at 60 Hz.    -   Galvanic isolation between input AC voltage and output voltages.    -   Cost of supply to be approximately $10.

Based on the desired parameters, the flyback converter topologyillustrated in FIG. 7 was chosen for the LED power supply 24. Theflyback converter circuit 80 is a well understood topology used inlighting applications. The reliability of this circuit is wellunderstood and sourcing components for this circuit in mass productionis expected to be cost effective. The flyback topology providesisolation and also allows adjustment of voltage conversion ratio throughthe turns ratio of the constituent transformer. The switching frequencyof the circuit can be chosen in the low 100s of kHz in order to effectreduction in size of the passive components.

The basic circuit 80 of a flyback converter is shown in FIG. 7. Thecircuit 80 includes an electromagnetic interference (EMI) filter 82, adamping network 84, a rectifier 86 to rectify the AC input voltage, anda transformer 88. The flyback transformer 88 converts an input voltage(with peak value V_(i)) to DC voltages V_(o) for the LEDs 42 and V_(cc)for auxiliary electronics that power house-keeping circuits (not shown)and also the power electronics 26 for the synthetic jets 18. A switch Q₁(here, the MOSFET 90, described further below) operates at the switchingfrequency of interest f_(sw). The transfer function of the flybackconverter 80 is:

$\begin{matrix}{\frac{V_{o}}{V_{i}} = {\frac{N_{s}}{N_{p}}\frac{D}{1 - D}}} & (1)\end{matrix}$

where N_(p) and N_(s) represent the primary and secondary turns of theflyback transformer 88 and D is the duty cycle of operating the switchQ₁. One important consideration in the design of this converter 80 wasthe ability to maintain a high power factor during operation. A flybackconverter operated in a discontinuous mode of operation achieves anatural power factor of 1. For example, a simple case of the flybackconverter 80 operated with duty cycle D₁ and time period T may beillustrative. If the flyback converter 80 is operated in thediscontinuous mode of operation, the current in the magnetizinginductance L will ramp linearly up to a peak value i_(pk) during thetime the switch Q₁ is on and then ramp linearly down to zero when theswitch Q₁ is off. If the inductor is sized appropriately, the inductorcurrent will reach zero before the start of the next cycle. At the endof the period D₁T the energy stored in the inductor can be representedas follows:

$\begin{matrix}{E = {\frac{1}{2}{Li}_{pk}^{2}}} & (2)\end{matrix}$

The value i_(pk) can be represented as

$\begin{matrix}{i_{pk} = {V_{i}\frac{D_{1}T}{L}}} & (3)\end{matrix}$

By substituting Equation (3) into Equation (2)

$\begin{matrix}\begin{matrix}{E = {\frac{1}{2}L\frac{V_{i}^{2}D_{1}^{2}T^{2}}{L^{2}}}} \\{= \frac{V_{i}^{2}D_{1}^{2}}{2{Lf}_{sw}^{2}}} \\{= \frac{V_{i}^{2}}{\frac{2{Lf}_{sw}^{2}}{D_{1}^{2}}}}\end{matrix} & (4)\end{matrix}$

The amount of power delivered to the load can thereby deduced as:

$\begin{matrix}\begin{matrix}{P_{load} = {E \times f_{sw}}} \\{= \frac{V_{i}^{2}D_{1}^{2}}{2{Lf}_{sw}^{2}}} \\{= \frac{V_{i}^{2}}{\frac{2{Lf}_{sw}}{D_{1}^{2}}}} \\{= \frac{V_{i}^{2}}{R_{hyp}}}\end{matrix} & (5)\end{matrix}$

For a power supply with an alternating input voltage of RMS value,V_(in-rms), the input power required by the power supply is

$\begin{matrix}{P_{in} = \frac{V_{{in}\text{-}{rms}}^{2}D_{1}^{2}}{2{Lf}_{sw}^{2}}} & (6)\end{matrix}$

Equation (6) was used to calculate the value of magnetizing inductance,L, for the flyback transformer 88. In order to do so, two designparameters—D₁ and f_(sw) were fixed. D₁ was set to a value of 0.5. Thevalue of f_(sw) was chosen for low conducted emissions. Severalstandards such as CISPR, IEC, FCC etc. are typically used to limit themaximum conducted emissions. Most of these applications imposeconstraints on conducted electromagnetic interference (EMI) between 150kHz and 30 MHz. In order to achieve high impedance to conductedemissions a switching frequency as close 150 kHz was chosen.

For example, at 140 kHz, a symmetric triangular switching ripple currentwould be expected to conduct currents at the odd harmonics of f_(sw).The first odd harmonic was expected to be 420 kHz. At this frequency,the impedance of the magnetizing inductance, L, was expected to besufficiently high to limit conducted harmonic currents. An efficiency(η) of 90% was assumed—the specified target efficiency. Based on theseparameters, the value of L was calculated as follows:

$\begin{matrix}\begin{matrix}{L = {\frac{V_{{in}\text{-}{rms}}^{2}D_{1}^{2}}{2f_{sw}}\frac{\eta}{P_{o}}}} \\{= {\frac{120^{2} \times 0.5^{2}}{2 \times 140 \times 10^{3}}\frac{90\%}{32.41}}} \\{= {360\mspace{14mu} {\mu H}}}\end{matrix} & (7)\end{matrix}$

TABLE 1 DESIGN PARAMETERS FOR FLYBACK POWER SUPPLY Switching frequency(fsw) 140 kHz Duty cycle for Q    0.5 RMS input voltage (Vin-rms) 120 VDC output voltage for LED power stage (Vo) ≈58 V Required output power(Po)  32.41 Target efficiency (η) 90% Magnetizing inductance required(L) 360 uH Turns ratio (N_(p):N_(a)) ≧2.9 Operating temperature ofconductor 100 C.

The turns ratio of the transformer 88 was calculated based upon therequirement for discontinuous mode of operation. From FIG. 7, the designcriterion for discontinuous conduction mode is

D ₁ T>D ₂ T  (8)

The method of volt-second balance across the magnetizing inductance willnecessitate

$\begin{matrix}{\frac{N_{p}}{N_{s}} > \frac{\left. {V_{{in}\text{-}{rms}} \times \sqrt{(}2} \right)}{V_{o}} > \frac{\left. {120 \times \sqrt{(}2} \right)}{58} > 2.9} & (9)\end{matrix}$

The turns ratio was designed to satisfy Equation (9). The design of thecore and windings for the flyback transformer was then completed. Theskin depth of copper at 100 C is 216 μm. In high frequency designs,proximity and eddy current losses can be significant and can degradeefficiency. Hence, litz wire was chosen in order to reduce the effect ofwinding losses. Based on analyses presented, litz-wire with AWG 44 (51μm diameter strands) strands was determined to be a feasible design.Typically, a strand diameter of 3× to 4× smaller than the skin-depth ofcopper helps maintain the resistance at high-frequency close to the DCresistance. The primary and secondary bundle configurations were chosenbased on RMS currents extracted from circuit simulation in LTSPICE [3],as well as commercial availability.

The high-voltage (HV) winding and low-voltage (LV) winding both sustaina low-frequency unipolar current at 60 Hz, and superimposed triangularcurrent at 140 kHz. The choice of strand dimensions was also guided bythe amount of area available for the windings. The maximum alloweddimension for the flyback transformer 88 was specified as 2.54 cm forthis application. An E-core geometry, E25/10/6, was chosen as thelargest core that would fit within constraints. The packing factor F forlitz winding with circular strands was estimated as follows:

$\begin{matrix}\begin{matrix}{F_{p} = {\frac{A_{circle}}{A_{square}} \times 0.5}} \\{= {\frac{\frac{a^{2}\pi}{4}}{a^{2}} \times 0.3}} \\{= 0.23}\end{matrix} & (10)\end{matrix}$

where A_(circle) represents the area occupied by circular strands ofdiameter a in a square section of side a. The factor of 0.5 was imposedto include the effect of insulation and bend radii of the litz bundle.The chosen strand diameter of 51 μm was implemented along with the areawinding window as follows:

$\begin{matrix}{A_{T} = {\frac{A_{w}}{2} \times F_{p} \times \frac{1}{N}}} & (11)\end{matrix}$

where A_(w) is the available winding area in the bobbin and A_(T) is thearea available for a single turn of a winding with N_(HV) turns. Thefactor of 2 applies to setting equal areas for the HV and LV windings ina 2-winding design in this application. With a fixed strand diameter(d_(s)), the number of strands required to fit in the winding window canbe calculated as follows:

$\begin{matrix}\begin{matrix}{N_{s} = \frac{A_{T}}{\frac{\pi}{4}d_{s}^{2}}} \\{= {\frac{A_{w}}{2} \times F_{p} \times \frac{1}{N_{HV}} \times \frac{4}{\pi \; d_{s}^{2}}}}\end{matrix} & (12)\end{matrix}$

The number of HV turns required was calculated. For a flybacktransformer operating in discontinuous conduction mode, the followingequation applies:

∫₀ ^(D) ¹ ^(T) V _(in)(t)=N _(HV) ×A _(core) ×B _(sat)  (13)

where V_(in)(t) represents the time varying unipolar input voltage thatimposes a unipolar magnetic flux in the magnetic core withcross-sectional area A_(core). The saturation flux density of thematerial is represented as B_(sat). At the peak of the input voltage,Equation (13) can be computed as:

$\begin{matrix}{{0.5 \times V_{{in}\text{-}{rms}} \times \sqrt{2} \times T} = \frac{0.5 \times V_{{in}\text{-}{rms}} \times \sqrt{2}}{f_{sw} \times N_{HV} \times A_{core} \times B_{sat}}} & (14)\end{matrix}$

The core material was chosen as 3C90 Ferrite based on datasheetrecommendations for 140 kHz operation and also based on commercialavailability at the time of design. The properties of the core are shownin Table II, below:

TABLE II PARAMETERS FOR E25/10/6, 3C90 CORE Switching frequency (fsw)140 kHz Assumed Operating temperature of core 100 C. Saturation fludensity (B_(aut)) 0.38 T Core x-sectional area (A_(core)) 39.5 × 10⁻⁶ m²Core volume 1930 × 10⁻⁹ m³

The number of HV turns was calculated from Equation (14) usingparameters in Table II as follows:

$\begin{matrix}\begin{matrix}{N_{HV} = \frac{0.5 \times V_{{in}\text{-}{rms}} \times \sqrt{2}}{f_{sw} \times A_{core} \times B_{sat}}} \\{= 41}\end{matrix} & (15)\end{matrix}$

The maximum allowed strands for the HV winding was calculated usingEquation 12 and as follows:

$\begin{matrix}{N_{s\text{-}{HV}} \leq {\frac{A_{w} \times F_{p}}{2}\frac{f_{sw} \times A_{core} \times B_{sat}}{0.5 \times V_{{in}\text{-}{rms}} \times \sqrt{2}} \times \frac{4}{\pi \; d_{s}^{2}}} \leq 78} & (16)\end{matrix}$

The number of turns N_(LV) for the LV winding was chosen to be 15 inorder to satisfy the equality in Equation (11). The maximum allowedstrands for the LV winding was calculated using Equation (12):

$\begin{matrix}{N_{s} \leq {\frac{A_{w}}{2} \times F_{p} \times \frac{1}{N_{LV}} \times \frac{4}{\pi \; d_{s}^{2}}} \leq 214} & (17)\end{matrix}$

Litz wire with 66 strands of AWG 44 and 150 strands of AWG 44 werechosen for the HV and LV windings respectively. These were the best-fitdesigns that were commercially available commercially available at thetime of design. This completes the design of the high frequencytransformer 88.

As will be appreciated, the leakage inductance of the transformer 88greatly affects the efficiency of the power supply. The transformer 88was interleaved in order to reduce leakage energy stored in the windingwindow. The winding build was implemented such that the LV winding waswound in two layers on either side of the HV winding. First, 8 turns of150/44 litz-wire (150 strands of AWG 44 litz construction) was woundaround a CPH-E25/10/6-1S-10P-Z bobbin. Next, 41 turns of 66/44 litz-wire(66 strands of AWG 44 litz construction) was wound, followed by 7 turnsof 150/44 litz-wire. The insulation on the litz-wire bundle was deemedsufficient for voltage isolation (an anticipated maximum of 2× of peakinput voltage of 170 V). In a design with no interleaving, the loss dueto leakage energy of the transformer was expected to be 0.5 W (about 2%of total loss). By interleaving the transformer, the loss was reduced by4× to 120 mW (about 0.4% of total loss). The transformer is expected todissipate approximately 5% of the total loss.

Referring still to FIG. 7, as described above, the switch Q₁ is a MOSFET90 in the circuit 80. Several commercially available MOSFETs wereinvestigated. The losses were estimated for each part based on voltageand current stresses obtained from circuit simulations. The switchingloss and conduction loss of several MOSFETs manufactured by FairchildSemiconductor Inc. were investigated. Fairchild Semiconductor parts wereinvestigated since they are already in use in other GE lighting products(e.g. PAR38 LED lamp). However, parts from other vendors may also besuitable.

The strategy of operating the flyback converter 80 in discontinuousconduction mode leads to high peak currents, particularly in the highfrequency ripple. Hence minimizing the channel resistance is critical.Also, the switching loss can be high at 140 kHz. The trade-offsassociated with both conduction loss and switching loss is shown inTable III, below:

TABLE III MOSFET LOSS CALCULATIONS V_(rated) I_(rated) 2xR_(dson)Cross-eff Ciss Pds-coss Pds-RdsLF Pds-RdsHF Pgs-ciss Ptotal $/unit Model(V) (A) mΩ (pF) (pF) (mW) (mW) (mW) (mW) (W) % Loss % ($) FCP16N60 60016 0.44 110 1730 400 46.8 79.1 24.2 0.55 1.84% 1.28 FCP11N60 600 11 0.6495 1148 350 68.0 115.1 16.1 0.55 1.82% 1.00 FCP4N60ND 600 7 1.06 60 710220 112.7 190.6 9.9 0.53 1.78% 0.73 FCP4N60ND 600 4 2 32 415 120 212.6359.6 5.8 0.70 2.32% 0.54 FQP8N60C 600 7.5 2.4 105 965 380 255.1 431.513.5 1.08 3.62% 0.42 FQP6N60C 600 5.5 4 65 620 240 425.1 719.1 8.7 1.394.64% 0.38

Based on the above-mentioned analysis, the MOSFET FCP4N60ND exhibits thelowest estimated loss. However, the MOSFETs, FCP11N60 and FCP16N60 arealso comparable in performance. The MOSFET, FCP11N60 was chosen based onavailability. This design is expected to dissipate about 2% of totalpower in the converter.

Referring now to FIG. 8, an example of a suitable circuit 92 that wasdesigned and tested for use as the synthetic jet power supply 26, of thedisclosed lighting system 10 is provided. As previously described, anarray of five synthetic jet devices (18) was included in the previouslydescribed embodiment. One exemplary circuit 92 of FIG. 8 was designed toinclude the following characteristics and parameters described in TableIV, below:

TABLE IV PARAMETERS FOR POWER CIRCUIT FOR SYNTHETIC JET. Parameter ValueExcitation frequency for jets 175 Hz sinusoidal DC Blocking capacitor(C₁) 44 pF Tantalum capacitor Resonant inductor (L) 0.1 mH at 400 Hz,Silicon Steel core ESR of L (R) 6.5 Ω at DC Tuning capacitor (C₂) 0.33uF Ceramic capacitor ESR per SJ (Rsj) 200 Ω Capacitance of 5 syntheticjets ≈500 nF in parallel (Csj) Expected power consumption by 0.5 Wsynthetic jet circuit

The circuit 92 provides a way to achieve the required drive conditions.The principle behind the circuit 92 is to drive a resonant circuit thatis formed with the synthetic jet devices 18. The synthetic jet 18 ismodeled by block 94, which includes a capacitor (C_(SJ)) with a seriesresistance (R_(SJ)) that represents the energy lost in physicallyactuating the synthetic jet 18. The resonant frequency is set to be thefrequency at which the synthetic jet 18 operates. This is achieved byusing an inductor (L) with a series resistance (R_(L)), and a capacitor(C₂). The capacitor, C₁, is a capacitor used to block the DC component.Any residual DC present at the output is attenuated by the resistor,R_(D). By virtue of the Q of the resonant circuit, peak voltage of thesquare voltage produced by the driver is amplified to provide therequired voltage at the output.

The circuit 92 includes a timer circuit 96 that can be assembled using acommercial chip to provide square voltage waveforms. A driver 98 isimplemented to buffer the timer 96 from the load 94 in case the outputcurrent drawn is beyond the capability of the timer circuit 96. Thecomponent, L, can be wound with a magnetic core and wire.

A single modeled synthetic jet 94 was experimentally characterized byapplying a sinusoidal voltage at the frequency of operation (175 Hz).The phase and magnitude of the impedance were calculated as the ratio ofthe measured voltage across and measured the current through the modeledjet 94. The modeled jet 94 was driven with an amplifier for thisexperiment. This value is representative of the value R_(SJ).

The expected performance of the prototype is shown in Table V.

TABLE V LOSS ESTIMATES FOR LED POWER SUPPLY Estimated loss intransformer 0.5-0.75 W Estimated loss in MOSFET 0.55 Estimated loss inauxiliary circuits 1.5 W Estimated loss in synthetic jet circuit 0.5 WPercentage loss w.r.t. output power ≈10%

As will be appreciated, various circuits may be provided as part of thedriver electronics 16, depending on the requirements. The circuits 80and 92 provide one example of suitable circuits to achieve theaforementioned goals.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A lighting system, comprising: a housing structure; a light sourceconfigured to provide illumination visible through an opening in thehousing structure; and a thermal management system configured to providecooling for the light source, the thermal management system comprising:a heat sink having a base and a plurality of fins extending from thebase; and one or more synthetic jet devices configured to generate andproject a series of fluid vortices toward the plurality of fins of theheat sink; wherein the housing structure includes an inlet air port andan outlet air port formed therein, with the one or more synthetic jetdevices being positioned adjacent the inlet air port such that ambientair is entrained into the housing structure through the inlet air port,flows across the fins of the heat sink, and is ejected out through theoutlet air port.
 2. The lighting system, as set forth in claim 1,wherein the base defines a lower plane of the heat sink and an upperedge of the plurality of fins that is distal from the base defines anupper plane of the heat sink; and wherein the one or more synthetic jetdevices are positioned so as to be between the lower and upper planes ofthe heat sink.
 3. The lighting system, as set forth in claim 1, whereinthe base is coupled to the light source and wherein the plurality offins extending from the base provide a plurality of air gaps therebetween.
 4. The lighting system, as set forth in claim 3, wherein atleast one of the plurality of fins has a respective synthetic jet deviceof the one or more synthetic jet devices coupled thereto.
 5. Thelighting system, as set forth in claim 4, wherein respective syntheticjet device is coupled to a respective fin such that the synthetic jetdevice is positioned at least partially within a respective one of theplurality of air gaps.
 6. The lighting system, as set forth in claim 3,wherein when the one or more synthetic jet devices are activated, aunidirectional air flow path is provided along each of the plurality ofair gaps, through a length of each of the plurality of fins.
 7. Thelighting system, as set forth in claim 1, wherein the housing structurecomprises: a cage having slots therein and configured to contain thedriver electronics; a thermal management system housing configured tocontain the thermal management system, with the thermal managementsystem housing including the inlet air port and the outlet air port; anda face plate having the opening formed therethrough through which the atleast one LED provides illumination.
 8. The lighting system, as setforth in claim 7, wherein a portion of the thermal management systemhousing flares out from the face plate to define the inlet air port andthe outlet air port.
 9. The lighting system, as set forth in claim 1,further comprising driver electronics configured to provide power toeach of the light source and the thermal management system.
 10. Thelighting system, as set forth in claim 8, wherein the light sourcecomprises at least one light emitting diode (LED) and wherein the driverelectronics comprises an LED power supply and a synthetic jet powersupply.
 11. A lighting system, comprising: an array of light emittingdiodes (LEDs) arranged on a surface of a lighting plate; a thermalmanagement system configured to provide cooling for the array of LEDs,the thermal management system comprising: a heat sink having a base anda plurality of fins extending from the base; and one or more syntheticjet devices configured to generate and project a series of fluidvortices toward the plurality of fins of the heat sink; and a housingstructure positioned about the array of LEDs and the thermal managementsystem, the housing structure including a thermal management systemhousing positioned about the thermal management system and including aninlet air port and an outlet air port formed therein; wherein the one ormore synthetic jet devices are positioned adjacent the inlet air portsuch that air is entrained into the thermal management system housingthrough the inlet air port and is ejected out through the outlet airport.
 12. The lighting system, as set forth in claim 11, wherein theplurality of fins defines a plurality of air gaps there between, andwherein each of the one or more synthetic jet devices is positioned atleast partially within a respective one of the plurality of air gaps.13. The lighting system, as set forth in claim 12, wherein when the oneor more synthetic jet devices are activated, a unidirectional air flowpath is provided along each of the plurality of air gaps, through alength of each of the plurality of fins.
 14. The lighting system, as setforth in claim 13, wherein ambient air is entrained into the thermalmanagement system housing through the inlet air port, passes across andis warmed by the plurality of fins, and is ejected out through theoutlet air port.
 15. The lighting system, as set forth in claim 11,wherein at least one of the plurality of fins has a respective syntheticjet device of the one or more synthetic jet devices coupled thereto. 16.The lighting system, as set forth in claim 11, wherein the inlet airport and the outlet air port are formed in the housing structure so asto be positioned adjacent the lighting plate.
 17. The lighting system,as set forth in claim 11, wherein the base of the heat sink is coupledto the surface of the lighting plate.
 18. A lighting system, comprising:a housing structure; a light source configured to provide illuminationvisible through an opening in the housing structure; a thermalmanagement system configured to provide a unidirectional air flowthrough the housing structure; and driver electronics configured toprovide power to each of the light source and the thermal managementsystem.
 19. The lighting system, as set forth in claim 18, wherein thethermal management system comprises: a heat sink; a plurality ofsynthetic jet devices; and a thermal management system housingpositioned about the heat sink and the plurality of synthetic jetdevices, the thermal management system housing including a duct systemcomprising ducts configured to intake or outtake ambient air.
 20. Thelighting system, as set forth in claim 18, wherein the plurality ofsynthetic jet devices are positioned proximate the duct through whichambient air is taken in, with the plurality of synthetic jet devicescausing the ambient air to flow across the heat sink and eject outthrough the outlet air port.